i7 Underclocking - How Low Can I Go?

[OhNoes!]

I have been inspired by a post on another forum about "process tweaks" and the "sweet spot" of cpus. We all know these things exist, but I for one, haven't bothered to find out; for one, I don't have a killawatt to do the stringent measurements. Another is time. To cut a long story short, I started experimenting with low clocks/voltage. The base clock setting range for my board (see sig.) is 100 - 600.

After many tries, I have managed to go as low as the 100 minimum base clock. I'm currently running 12x100 for 1.20GHZ. This is bios bootable with 0.688v and prime stable (any lower voltage, results in a blue-screen during windows boot - so it seems this is the absolute limit for my system - I say system because I don't know if it's the motherboard or cpu crapping out due to low power signal).

I have tried setfsb, but it detects 600, instead of 100. I'm thinking it's because the bios range is cyclical eg. after 100, 600 and vise-versa.

So my question is, has anyone gone lower than this? Is this a programming issue? Could it be by-passed. Underclocking is quite adictive.

By the way, underclocking i7 below stock is pointless, unless heat is an issue. See the two results below:

Mandatory CPU-Z Screenshot


32bit Prime95 blend with 0.688v @ 1.2GHZ


32bit Prime95 blend with 0.960v @ 2.8GHZ (about 118% more processing power with only 0.272v more). I know this is not the whole story as there laws of physics that need to be taken into consideration here - transistor limitations and such.

[rusty]

please enlighten me why would you do such a thing as underclocking?

[saaya]

to save power i guess...?
but its only a few watts, maybe 40W at most... so i dont see the point here either... in laptops it makes sense, but on a desktop...

on BR bclock goes as low as 80mhz, but vcore cant be reduced below stock...
i think gigabyte can reach 90mhz bclocks as well... asus cant iirc...

[Envy]

pretty nice i underclock my Q6600 to build a NAS after that i like to underclock my systems as much as i overclock it for the fun to know how low i can go

[OhNoes!]

please enlighten me why would you do such a thing as underclocking?

There are a few reasons; cut down on power consumption, heat output, and to run low rpm fans or passive cooling for silent computing, are some of the few things that come to mind readily. I have been running my system at 1.2GHZ, DDR3 1600 (6-8-6-20) for the last few days and it's really fun and equally as fast as 4.2GHZ with same ram timings for everything I've been using the computer for.

to save power i guess...?
but its only a few watts, maybe 40W at most... so i dont see the point here either... in laptops it makes sense, but on a desktop...

on BR bclock goes as low as 80mhz, but vcore cant be reduced below stock...
i think gigabyte can reach 90mhz bclocks as well... asus cant iirc...

Yeah, as I pointed out in my op, the voltage dissimilarity between a 1.2GHZ and 2.8GHZ is so insignificant that it'll be better to undervolt while maintaining stock clocks. But it's kinda cool to be able to do this. I loved it. Personally, these are the lowest clocks and voltages I've seen on any Core i7 setup. Plus, it is perhaps more dangerous to underclock/undervolt than to overclock so it makes for a nice bragging rights.

pretty nice i underclock my Q6600 to build a NAS after that i like to underclock my systems as much as i overclock it for the fun to know how low i can go

I know, I'm quite addicted already.

[informal]

This is not without reason,I can understand the reasoning behind this line of thinking : power consumption ,heat,low rpm fans etc. I ,for example,run my 10h at 600Mhz and 0.7V while in idle...It sits nice and cool,the board is much cooler.The whole PC is silent,fans don't spin at all (except on my Radeon 4850 gfx card,but it's low rpm). When I need power i switch to higher speed profile via small app(k10stat) and voila I have 3+Ghz when I need it. It's a smart way of managing your electric bill.

[8800's@over]

I try to undervolting at 3.0GHz in my 930. LinX stable @ 0.95v !

[TJ TRICHEESE]

this sounds horrible, not overclocking is bad enough but backwards overclocking is hard to comprehend

[OhNoes!]

This is not without reason,I can understand the reasoning behind this line of thinking : power consumption ,heat,low rpm fans etc. I ,for example,run my 10h at 600Mhz and 0.7V while in idle...It sits nice and cool,the board is much cooler.The whole PC is silent,fans don't spin at all (except on my Radeon 4850 gfx card,but it's low rpm). When I need power i switch to higher speed profile via small app(k10stat) and voila I have 3+Ghz when I need it. It's a smart way of managing your electric bill.

That sounds cool. I doubt I can do that on my board. I'm sure the higher end EVGA, Asus, Gigabyte allow on the fly over/underclocking.

this sounds horrible, not overclocking is bad enough but backwards overclocking is hard to comprehend

Gives a new meaning to extreme, doesn't it? Extreme overclocking in the opposite direction.

I try to undervolting at 3.0GHz in my 930. LinX stable @ 0.95v !

Here's what I just did, I'll try bumping up clocks a bit to see how it goes.

Windows Server 2008 Enterprise x64 running Prime 95 64bit

[famish99]

Plus, it is perhaps more dangerous to underclock/undervolt than to overclock so it makes for a nice bragging rights.

I know, I'm quite addicted already.

Agreed, I've never destroyed a board while overclocking, but undervolting/underclocking I've gone threw a few boards already on my amd htpc machine.

I do have a killawatt and it was extremely addictive to see a quadcore phenom 2 system use less than 100w under linx! I'm now inspired to see what I am capable of doing on my i7, but I doubt I would be able to get my total power consumption below 200w under load, since I have a gtx 275, watercooling loop, and 16 phase mobo.

[OhNoes!]

Agreed, I've never destroyed a board while overclocking, but undervolting/underclocking I've gone threw a few boards already on my amd htpc machine.

I do have a killawatt and it was extremely addictive to see a quadcore phenom 2 system use less than 100w under linx! I'm now inspired to see what I am capable of doing on my i7, but I doubt I would be able to get my total power consumption below 200w under load, since I have a gtx 275, watercooling loop, and 16 phase mobo.

Hmm, could you try 12x 133 and do a comparison with stock clocks and your regular 24/7 power consumption numbers?

[famish99]

Hmm, could you try 12x 133 and do a comparison with stock clocks and your regular 24/7 power consumption numbers?

Do you want me to try that with stock volt or undervolted?

[Chumbucket843]

you wont get much lower than ~.7 volts. cmos transistors wont work past that. the power of other components will make the benefit of underclocking less and less useful.

[OhNoes!]

Do you want me to try that with stock volt or undervolted?

undervolted, stock, and overvolted for the various clocks, if you could, please.

you wont get much lower than ~.7 volts. cmos transistors wont work past that. the power of other components will make the benefit of underclocking less and less useful.

I agree. I was mainly looking to go lower than 100 base-clock limit. I don't know if this is hard-coded into the pll or if it's just a bios thing (not that the two are different in any regard), but at 100 bclk, even setfsb seems to have problems reading the bclk right.

[Musho]

Agreed, I've never destroyed a board while overclocking, but undervolting/underclocking I've gone threw a few boards already on my amd htpc machine.

I do have a killawatt and it was extremely addictive to see a quadcore phenom 2 system use less than 100w under linx! I'm now inspired to see what I am capable of doing on my i7, but I doubt I would be able to get my total power consumption below 200w under load, since I have a gtx 275, watercooling loop, and 16 phase mobo.

Are you sure that wasn't just bad luck? Why would underclocking hurt hardware? I can see why overclocking could hurt it, but it's already extremely difficult to purposely kill hardware without using excessive voltage... Makes me wonder why it's so dangerous to underclock

[rusty]

why not to buy a cheap chip for underclocking ? you need all 8 cores to do htpc :> wow

[famish99]

Are you sure that wasn't just bad luck? Why would underclocking hurt hardware? I can see why overclocking could hurt it, but it's already extremely difficult to purposely kill hardware without using excessive voltage... Makes me wonder why it's so dangerous to underclock

Everything is spec'd to run within a certain range, including motherboard components. It's a little scary running them low voltage because vrm's are spec by current. The lower the voltage, the more current the chip can draw given a specific power level, the more likely you can burn something out. Granted this is still a lot of speculation because of all the variables that come into play such as the fact that power does tend to reduce as you drop voltage and the fact that it was a cheap mobo to begin with. But don't think you can only break things going the high end, low end is just as destructive.

[saaya]

these are the lowest clocks and voltages I've seen on any Core i7 setup.

uhm... all you did was lower the bclock to 100... in idle all 45nm chips drop to 12x multi... ive seen people run 85mhz bclocks and in idle that results in around 1ghz clocks... plus 32nm chips have a lower idle multi, at least the mobile ones, not sure about desktop...

a 45nm 1366 cpu is def not the right chip if your into underclocking man
afaik theres a way to enable 4x multis on c2d desktop cpus, and i think amd can run really low multis as well, with a really low ref clock...

a c2d should be able to run an fsb of 100mhz or less, with a multi of 4... so thats 400mhz or less... just fyi...

[OhNoes!]

uhm... all you did was lower the bclock to 100... in idle all 45nm chips drop to 12x multi... ive seen people run 85mhz bclocks and in idle that results in around 1ghz clocks... plus 32nm chips have a lower idle multi, at least the mobile ones, not sure about desktop...

a 45nm 1366 cpu is def not the right chip if your into underclocking man
afaik theres a way to enable 4x multis on c2d desktop cpus, and i think amd can run really low multis as well, with a really low ref clock...

a c2d should be able to run an fsb of 100mhz or less, with a multi of 4... so thats 400mhz or less... just fyi...

This is not my interest either, I'm trying to find my chip's "sweet-spot.:"

By the way, the comment you quoted was meant for desktop chips. Care to post a screenshot? Better yet, you have an i7 system so post your own ss if you can't find another on the internet.

[cstkl1]

more interesting would be
how low can u clock ure ram at 1.35v

[famish99]

more interesting would be
how low can u clock ure ram at 1.35v

I fail to see how that's more interesting than underclocking the cpu. You run into all of the same boundaries you have with the cpu (ie minimum bclk and multiplier availability). DDR3 already uses an insanely low amount of power as it is.

Don't get me wrong, I realize the pointlessness of underclocking an i7, but as an experiment, it's entertaining. In addition, just because you don't run the chip slower, doesn't mean Intel hasn't, the slow speed edge is just as important to find as the fast speed edge. You can run into all sorts of interesting issues at the low end as you do on the high end.

[Aedubber]

There is watercooled setups that can run silent and still overclock .. Personally if your using save money on an electric bill then u shouldn't even own a comp .. I mean how much are u saving really??

[WhiteFireDragon]

sweat spot i found is a slight overclock while undervolting. my i7 cruncher runs at 3.7ghz while undervolted to something like 1.13v

[Splave]

hey op why dont you see how long it lasts with no cooler on it at those volts!

[famish99]

hey op why dont you see how long it lasts with no cooler on it at those volts!

Not very long, we managed to literally melt the socket of one of our boards at work with an embedded 30w tdp part when we forgot to seat the cooler correctly, there's little hope that an i7 would fare better even when undervolted.